Structure of artificial bone material for use in implantation

ABSTRACT

There is provided a structure of artificial bone for use in implanting or grafting bone comprising; a sintered body of calcium phosphate compounds; and hollowed minute tubes in said sintered body, having very small diameter, and extending along with a direction of Haversian canal extension of live organism, so as to produce two dimensional close-packed structure in said body, in form of cubic or hexagonal arrangement. The arrangement has in the sintered body of calcium phosphate compounds; hollowed minute tubes having a diameter of 0.1 to 2.0 mm, and the major portions thereof extending along with a direction of the Haversian canal extension, and producing a two dimensional close packed arrangement in said body against the face vertical to said direction, and being arranged with a separation, distance of 1.0 to 5.0 mm. The structure has preferably really spherical pores having diameter of 50 to 600 micrometer, and the porosity thereof being 0.5 to 40 percent.

FIELD OF ART

The present invention relates to a structure of artificial bones for usein bone implantation or grafting, formed from calcium phosphatecompounds. Particularly, it relates to an artificial bone structure foruse in bone implantation or grafting, which can be applied at a boneposition to which load or force is applied, and is useful in the medicalfields especially in orthopaedics, plastics and oral surgery.

BACKGROUND OF THE ART

Compounds of calcium phosphate, including hydroxyapatite and tricalciumphosphate have the similar chemical properties to those of live bone andteeth in a living body or organism. The sintered body thereof has goodbio-compatibility, and then, can be used as an alternative material usedfor artificial bone, bone aid and artificial roots, in form of a denseor porous body.

Such conventional calcium phosphate structure in dense body form canhave enough strength necessary to support biologically dynamic movement,whereas there is not found new bone growth nor generation of bone tissueinto the artificial dense bone structure. Further, generally, theadherent force to the living tissue where the artificial bones areinserted or implanted is dependent on the adhering force at the smoothinterface thereof, and then it can not have the adherent function orforce higher than that expected therefrom. On the other hand, a porousbody of calcium phosphate compounds has somehow a limit of the dynamicstrength, and then implantation of such porous body into a bone site ofapplied weight or load should be avoided, and sole use of the porousbody should be avoided.

In order to enable sole use of an artificial bones at a bone site ofapplied mechanical load, it is necessary to provide a calcium phosphatecompound to produce organization and structure having goodbio-compatibility, and a method of compounding with organic or inorganicelastic material, and further to provide a material in use forcompounding or integrating with the biological material. Such material,or porous ceramic material is disclosed in Japanese Patent ApplicationNo. 60-16879/1985.

DISCLOSURE OF INVENTION

The subject to be solved technologically by the present invention is theprovision of the strong and tough structure of artificial bone producedfrom calcium phosphate compounds in which bone can be newly organized orgrown into the bone structure, and then the artificial bone is welladhered to biological organism formation, and new bone organization canbe well developed into the artificial bone.

Then, it is an object of the present invention to provide an artificialbone structure of calcium phosphate compounds which can evidence highmechanical strength when implanted in a bone tissue.

The inventive structure of artificial bone for use in implantation isprovided for solving the above mentioned subject, and the presentinvention resides in a new structure of artificial bone for use inimplantation or grafting of the bone, comprising a sintered body ofcalcium phosphate compounds: and hollowed minute tubes having diametersof 0.1 to 2.0 mm, and the major portions thereof extending along with adirection of Haversian canal extension, and producing two dimensionalclosely packed arrangements in said body against the surface vertical tosaid direction, and being arranged with separation, distances of 1.0 to5.0 mm. Preferably, the internal structure of said sintered body hasreally spherical pores having diameters of 50 to 600 micrometers, andthe porosity of said structure is preferably 0.5 to 40 percent.

Hereinafter, "calcium phosphate compounds" may include hydroxyapatite,tricalcium phosphate, tetracalcium phosphate, and further calciumphosphate compounds which can constitute the artificial bone.

SIMPLE DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B illustrate schematically the representative structure ofthe inventive artificial bone for use in implanting or grafting bone,which can have high strength and toughness.

FIG. 2 illustrates schematically the sectional view of the inventivestructure of the artificial bone.

FIG. 3 illustrates schematically the living bone to which the inventivestructure of calcium phosphate compounds was actually applied with highstrength.

FIGS. 4A and 4B illustrate the close-packed arrangement of the hollowedtubes therein, and FIG. 4A shows the close-packed arrangement of thetubes in cubic form while FIG. 4B shows the close packing in hexagonalarrangement.

BEST MODE FOR CARRYING OUT THE INVENTION

The starting material for producing the inventive structure having highstrength, and high toughness may be porous bone ceramic material, forexample, the ceramic material as disclosed in Japanese Patent Laid-openPublication No. 60-16879/1985. The present invention provides a specificstructure to be applied to such material. The invention resides in thestructure of the material for artificial bones, having a function toimprove bio-compatibility and fusion ability to an organism or livetissue, which structure can be formed by providing small diametertubular holes in one predetermined direction into a green body orsintered body in a process of manufacturing artificial bones fromorganic material, which holes can ensure growth of new bone tissue afterimplanted, and well flowing blood so as to grow uniformly new bonetissue.

The composition or structures of the tubular holes provided in providesone certain direction in the new structure of artificial bones are shownin FIGS. 1 to 4, can be explained as follows:

The small diameter tubular holes have preferably a diameter; d, as shownin FIG. 4, ranging 0.1 to 2.0 mm, and a suspension distance D, betweenthe holes, as shown in FIG. 4, ranging 1.0 to 5.0 mm. More preferably,the diameter d is 1.0 to 3.0, and the distance D is 1.0 to 3.0 mm.

When the diameter d is lower than 0.1 mm, it will be possibly lower thanthe diameter of the bone tissue unit (osteon) including a Haversiancanal, and then, is not preferable. When the diameter d is higher than2.0 mm, the strength of the bone will be lowered, and then is notpractical.

When the separation distance D is lower than 1.0 mm, the strength willbe lowered similarly as above. When the distance D is higher than 3.0mm, less number of Haversian canals can be formed to generate blood flowin the bone, and the distance is too great so that the uniform bloodflow can not be generated.

The tubular holes extend in a certain direction, which is correspondingto the direction along which Haversian canals extend. The arrangement ofthe tubular holes is that they are arranged in a close packing in aplane vertical to the direction in which the holes extends. Theclose-packed structure is as shown in FIGS. 4A and 4B, wherein FIG. 4Ashows two dimensional cubic arrangement, and FIG. 4B shows twodimensional hexagonal arrangement. The distribution of the holes 2 isclose-packed in a plane vertical to the direction along with which theyextend. Such two-dimensional close packed structure is one of twoalternatives, one is that the circles formed by the centers of the holesas a center of the circles are packed to form perfect squares, as shownin FIG. 4A, and the other is that the centers of the holes are packed toform perfect hexagons as shown in FIG. 4B.

The artificial bone implanted in a living body or organism, blood willflow in the tubular holes 2, in the structure as shown in FIGS. 4A and4B, and then, bone formation is expected to grow around the holes 2, andtherefore, there will be found new bone tissue growing easily in thestructure of the implanted bone after implantation of the inventiveartificial bone. In the other words, blood will flow uniformly in thestructure of the implanted artificial bone, and will supply enoughnutrient in the implanted artificial bone structure, so as to developgeneration and growth of live bone tissue by activating osteoblast.Therefore, this can improve bio-compatability and fusion with livetissue. Then, new bone formation will rapidly develop, and then, willimprove complex strength of the artificial bone structure, and theadherent force with the bone surface can be ensured, and it will enablesole use at the site of applied dynamic load or force.

The material which can constitute the inventive bone structure can beproduced, for example, as follows: a slurry of calcium hydroxide ismixed with phosphoric acid by titration, and by adjusting a reactiontemperature, pH of the liquid so as to form hydroxyapatite, and theapatite is molded in a certain shape, which is fired into a sinteredbody.

As a starting material for the formation of the inventive bonestructure, preferably the molar ratio of calcium to phosphorous is therange of 1.0 to 2.0 in the calcium phosphate compounds.

When the Ca/P molar ratio is less than 1.0, phosphoric acid willliberate to instabilize the compounds chemically. When the Ca/P molarratio is higher than 2.0, calcium oxide will produced during firing asdecomposition of the compound, and it will stimulate strongly theorganism when implanted in the organism, thereby generating inflammationin the organism. Therefore, the range above 2.0 of Ca/P molar can not beused. Because of the above mentioned reasons, the preferable range forthe Ca/P molar ratio is 1.0 to 2.0.

A concrete method of producing small diameter tubular holes inaccordance with the present invention may comprise drilling holesextending in a certain direction, in a formed and sintered body ofphosphate compound synthesized as mentioned above, by using a drill bar,and alternatively molding the material into a structure having smalldiameter tubular holes by using injection molding, or extrusion molding,or alternatively the process comprising molding the material into thestructure containing resin fibers, and then burning the formed body soas to burn out the fibers in the body thereby producing small diametertubular holes.

The method of producing a porous body of calcium phosphate compounds inaccordance with the present invention will involve forming a sinteredbody containing spherical pores, and one of such formation processcomprises forming a green body containing synthetic resin beads therein,and firing the green body so as to burn out the beads thereby producingspherical pores in the resulting fired body of calcium phosphatecompounds. Further, synthetic fibers can be contained or mixed in thegreen body so as to form hollowed intercommunications, thereby enablingto produce the combination of spherical pores and intercommunications inthe sintered structure. Therefore, as a synthetic resin, at least one ofpolypropylene, polymethylmethacrylate, polystyrene and polyethylene canbe used.

The porosity depending on the spherical pores, in the sintered body ispreferably 0.5 to 40 percent, and more preferably 5 to 35 percent. Whenthe porosity is lower than 0.5 percent, the ratio of the interconnectionof the pores is lowered. When the porosity is higher than 40 percent,the strength of the sintered body will be not enough to support the bonestructure.

The inventive structure of artificial bones is illustrated in referenceto the drawings. FIGS. 1A and 1B show a representative artificial bonefor use in implantation, with high strength, as obtained in accordancewith the present invention. A number of small diameter tubular holes 2are provided in a certain direction in a sintered porous body of calciumphosphate, and further, among them a number of pores of sphere 3 and anumber of hollowed intercommunications are provided in the body. FIG. 1Ashows a cube 1 of the inventive artificial bone structure, from whichdesired shape of bones can be produced by machining. Alternatively, thedesired shape of the bone can be produced by molding initially thematerial into the desired shape shown in FIG. 1B. The desired shape ofthe inventive bone can be used for implantation into a living bone ororgan. FIG. 2 is a sectional view showing an internal structure of theinventive artificial bone structure. A number of small diameter holes orhollow tubes 2 extending in a certain direction are produced in theporous sintered body of calcium phosphate compounds by drilling the bodyof phosphate compounds or molding into a sintered body of phosphatecompounds having a number of spherical pores 3 and hallowedintercommunications (not shown).

In FIGS. 1, 2, 3 and 4, 1 depicts a sintered body of calcium phosphatecompounds, 2 depicts tubular holes or hollow tubes, 3 depicts pores ofsphere, and 4 depicts the artificial bone used for implantation.

The structure of the artificial bone for use in implantation accordingto the present invention can be applied to insert, fill up, or cover adefect or removed portion of a living bone, and then new bone tissue canbe expected to grow in a short time so as to produce enough strength ofthe artificial bone structure.

The bone structure of the present invention and the process formanufacturing the same are detailedly illustrated by the followingexample, which should not be interpreted for the limitation of theinvention.

EXAMPLE

Powder of hydroxyapatite having a molar ratio of Ca to P of 1.67, asprepared by a wet process was mixed with spherical beads having diametera of 50 to 250 micrometers, of methylmetharylate resin, and further pile(hair) of animal (cat) having diameter a of 5 micrometers and length of50 micrometers, and the resulting mixture slurry was pressed at roomtemperature under Cold Isotropic Pressing of 300 kgf/cm² into a certainshape. The resulting shaped body was further cut into a cube of 20 mm,and the tubular holes were provided with a separation distance betweenthe holes of about 3.0 mm, so as to form a green body. This green bodyis put in burning powder, and then sintered for about one hour at 1,150°C., and then, machined into a cube of 15 mm. This has a pressurestrength of 800 kgf/cm².

The resulting artificial bone structure was used for implantation into aadult dog. A portion of (Corpus) tibia of the adult dog was removed atthe edge of the inner portion in the length of 15 mm, in almost 3/5 ofthe sectional area, as shown in FIG. 3, and the inventive artificialbone cube produced as illustrated above was cut in an appropriate shapeto the removed hollowed portion of the tibia, and the artificial bonewas implanted into the tibia, as shown in FIG. 3. In the other words,the inventive bone structure 4 for use in implantation having smalldiameter tubular holes extending in one direction was implanted in thetibia bone 5 with matching the direction of the hole extension to thedirection of Haversian canals extending in the live tibia bone 5.

At eight weeks after implantation, Xray observation revealed that aclear zone due to the removed bone disappeared. After 52 weeks passed,there was not found any defects such as crack, and damage in the bone.

The strength of the implanted bone was measured, and revealed that thepressure strength in one direction was 1,100 kgf/cm², and 1,150 kgf/cm²respectively when 12 weeks and 26 weeks passed after the operation. Itrevealed out that the inventive artificial bone structure has enoughstrength to support the dynamic load and durability.

The inventive structure of the artificial bone for implantation has beenfound to have the following function and effect.

Firstly, the holes extending along Haversian canals extending in thebone constitute bone acceptance holes in which blood can flow, therebyincreasing the flow of blood in the bone and further developing theadherent force to the live tissue. Secondly, it can provide improvedaffinity and bio-compatibility with the live tissue, and can be appliedsolely to the situation at which weighting load is applied. Thirdly, newbone formation can grow rapidly in the implanted bone structure, andtherefore, the strength of the bone complex structure can be rapidlyincreased, and at the same time the adherent force to the live bone willbe developed and maintained. Therefore, it provides highly strong bonecomplex or structure.

Industrial Utilization

The inventive structure of artificial bone for use in implanting orgrafting bone in a living body has the following industrial utilization.

Firstly, the holes extending along Haversian canals extending in thebone constitute bone acceptance holes in which blood can flow, therebyincreasing the flow of blood in the bone and further developing theadherent force to the live tissue.

Secondly, it can provide improved affinity and bio-compatibility withthe live tissue, and can be applied solely to the situation at whichweighting load is applied.

Thirdly, new bone tissue can grow rapidly in the implanted bonestructure, and therefore, the strength of the bone complex structure canbe rapidly increased, and at the same time the adherent force to thelive bone will be developed and maintained. Therefore, it provideshighly strong bone complex or structure.

We claim:
 1. A structure of artificial bone for use in implanting orgrafting bone, comprising:a sintered body of calcium phosphate compoundshaving spherical pores and hollowed intercommunications between poreshaving diameters of the order of a few micrometers, with hollowed minutetubes extending through said sintered body, having diameters of 0.1 to2.0 mm, and extending along a direction of Haversian canals of a liveorganism for supporting the flow of blood for developing adherent forceto the live organism, the tubes being spaced from one to five mm toproduce close packing structure and high strength in said body.
 2. Thestructure in accordance with claim 1, wherein said sintered body hasspherical pores having diameter of 50 to 600 micrometer, and theporosity of said structure is 0.5 to 40 percent.
 3. A structure ofartificial bone, for use in implanting or grafting bone comprising:asintered body of calcium phosphate compounds having spherical pores andhollowed intercommunications between the pores having diameters of theorder of a few micrometers, and hollowed minute tubes formed in saidsintered body, having diameter of 0.1 to 2.0 mm with axes thereof forextending along a direction of Haversian canals of a live organism tosupport a flow of blood encouraging development of an adherent force,and producing a two dimensional closely packed arrangement in said bodyin a plane normal to said direction having separation, distances of 1.0to 5.0 mm.